Some interesting, factual and documented info here, but I don't think the mics in the vid I posted are the feedback-cancelling scheme- the Pro-Sound forum post says the mics had to be near-perfectly matched, and those mics in the vid don't appear to even be the same brand.
Thanks for the link to the Pro-sound forum- as I am doing live sound setups/gear/etc. I probably should be in that forum, instead of here...